From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B822BC6FD1D for ; Tue, 21 Mar 2023 17:32:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229997AbjCURca (ORCPT ); Tue, 21 Mar 2023 13:32:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43772 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229571AbjCURc1 (ORCPT ); Tue, 21 Mar 2023 13:32:27 -0400 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A170B13D5C; Tue, 21 Mar 2023 10:32:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=xUZFSZQsr16SNSQJKusTXYyu832nutqEq5J/FsHnccU=; b=AVftADjchhmt+Jp4bRXmDpPWgb QPWGGGotXG4NW1Bxs8o7Mp2rYgt/rL0QpXwz7h7on7QEc0WLk1BogpwK3a4peFkSHmTxBkVUyXocp j16OfEx0Oa09g8pUR/qFB7nkgAKzV/AW/0T7oiuhW2LiRPbNE7GT6NZmc/fLBVcY22b/BpDYwIOMJ 2N+0YvkAiRDtyivAXO6s+QL9tNvKIH+3z2wm6TRGR2P1oF6tdGWQwzSQ2WpgY5ufuJR9Gx3RyzHQF kR1xJKNsXr60PT+/7CeaDjk9yyvTwktOC8fZrAOTP1SzL9jUPDeglbIOlB9HuOkQdulRWp8kKMoJC oqAmnEXA==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:51692) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1pefq5-0001da-I2; Tue, 21 Mar 2023 17:32:01 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1pefpp-0007vh-5A; Tue, 21 Mar 2023 17:31:45 +0000 Date: Tue, 21 Mar 2023 17:31:45 +0000 From: "Russell King (Oracle)" To: Donglin Peng Cc: mhiramat@kernel.org, rostedt@goodmis.org, mark.rutland@arm.com, will@kernel.org, catalin.marinas@arm.com, palmer@dabbelt.com, paul.walmsley@sifive.com, tglx@linutronix.de, dave.hansen@linux.intel.com, x86@kernel.org, mingo@redhat.com, xiehuan09@gmail.com, dinghui@sangfor.com.cn, huangcun@sangfor.com.cn, dolinux.peng@gmail.com, linux-trace-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 1/2] function_graph: Support recording and printing the return value of function Message-ID: References: <20230320131650.482594-1-pengdonglin@sangfor.com.cn> <20230320131650.482594-2-pengdonglin@sangfor.com.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230320131650.482594-2-pengdonglin@sangfor.com.cn> Sender: Russell King (Oracle) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 20, 2023 at 06:16:49AM -0700, Donglin Peng wrote: > diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S > index 3e7bcaca5e07..ba1986e27af8 100644 > --- a/arch/arm/kernel/entry-ftrace.S > +++ b/arch/arm/kernel/entry-ftrace.S > @@ -258,7 +258,15 @@ ENDPROC(ftrace_graph_regs_caller) > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > ENTRY(return_to_handler) > stmdb sp!, {r0-r3} > +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL > + /* > + * Pass both the function return values in the register r0 and r1 > + * to ftrace_return_to_handler > + */ > + add r2, sp, #16 @ sp at exit of instrumented routine > +#else > add r0, sp, #16 @ sp at exit of instrumented routine > +#endif > bl ftrace_return_to_handler ... > -unsigned long ftrace_return_to_handler(unsigned long frame_pointer) > +static unsigned long __ftrace_return_to_handler(unsigned long retval_1st, > + unsigned long retval_2nd, unsigned long frame_pointer) ... > +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL > +unsigned long ftrace_return_to_handler(unsigned long retval_1st, > + unsigned long retval_2nd, unsigned long frame_pointer) > +{ > + return __ftrace_return_to_handler(retval_1st, retval_2nd, frame_pointer); > +} > +#else > +unsigned long ftrace_return_to_handler(unsigned long frame_pointer) > +{ > + return __ftrace_return_to_handler(0, 0, frame_pointer); > +} > +#endif > + Hi, To echo Mark's criticism, I also don't like this. I feel it would be better if ftrace_return_to_handler() always took the same arguments irrespective of the setting of CONFIG_FUNCTION_GRAPH_RETVAL. On 32-bit ARM, we have to stack r0-r3 anyway to prevent the call to ftrace_return_to_handler() corrupting the return value, and these are the registers we need. So we might as well pass a pointer to these stacked registers. Whether that's acceptable on other architectures, I couldn't say. Thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!